1. Field of the Invention
This application relates to an underground storage tank having an access dome assembly and, more specifically, an underground storage tank wherein the access dome assembly is raised above the bulk of the underground storage tank.
2. Background Information
Underground storage tanks may be used for storing fuel, such as, but not limited to, propane which is used for heat within a home or business. The tanks include a sidewall defining an enclosed space in which the fuel is stored. The sidewall is typically an elongated cylinder having two hemispherical end lids. Such tanks are typically buried about one to two feet under the ground surface with the longitudinal axis extending generally horizontal. The tanks also typically include an access assembly having a fuel line, a withdrawal line and a dome assembly. The dome assembly extends upward from the tank and protrudes slightly above the ground surface. Within the dome assembly are the fuel line and the liquid withdrawal line. The fuel line is used to fill the vessel assembly with liquid fuel and to extract fuel gas. That is, within the vessel assembly, a portion of the fuel vaporizes and the fuel vapor is extracted to be used. The liquid withdrawal line is used to extract the liquid fuel if the tank needs to be emptied rapidly. Generally, the fuel line is raised above the surface of the vessel so that the fuel line connections may be accessed by a user. The liquid withdrawal line is generally flush with the vessel assembly so as to lessen the chance that the withdrawal line will be damaged. Other components of the tank, such as a control assembly (couplings for use devices, valves, gauges, and other such devices or structures) and a required data plate, are also disposed within the dome assembly. The dome assembly typically includes an elongated collar and a lid. The collar, which is typically cylindrical, extends from the vessel assembly sidewall to a point just above the ground surface. The lid is hinged to the collar.
One disadvantage of this configuration is that the depth at which the tank may be buried is controlled by the length of the collar. That is, the collar may not be too long otherwise a human would not be able to access certain components such as the data plate and the withdrawal line located on the vessel sidewall. Also, in this configuration, the coupling of the dome assembly to the vessel sidewall is difficult. That is, as noted above, the vessel sidewall is typically a horizontal cylinder while the dome assembly is a vertical cylinder. Thus, the intersection of these two cylinders is a complex line. As such, the fit between the dome assembly and the vessel assembly are difficult to seal.
There is, therefore, a need for an underground storage tank wherein the dome assembly does not need to be attached to the vessel assembly.
There is a further need for an underground storage tank wherein the withdrawal line includes a pressure relief device so that the withdrawal line may extend above the vessel assembly.